In general overview, guided earth boring is required to bore long holes for reception of gas lines, electrical conduits, communication conduits, etc.
In a conventional manner, a series of drill pipes, which collectively form a drill string when interconnected, are joined to a motor for rotating the same. At an opposite end, a bit, reamer or percussion device is connected to permit the drilling. Clearly, the greater the horizontal distance becomes, the greater the number of drill pipes associated with the drill string. With greater length, coupled with the fact that enormous forces are involved at the drilling bit, there is a high degree of kinking and flexing in the drill string. The result is that the forces from this motion is translated to the drill string motor and the support thereof.
The effect of the irregular motion of the drill string is most pronounced at the drill face. The drill bit is incapable of drilling a substantially horizontal bore and further, the dimension of the bore enlarges due to the lack of control at the drilling face.
The prior art has set forth a host of patents which relate to apparatuses to effect horizontal drilling, typical of which is U.S. Pat. No. 4,953,638. The patent teaches an apparatus including a channel bearing frame for receiving a wheeled drill string motor. There is no provision for any lateral or elevational tolerance when the motor is carried by the carriage. Accordingly, this reference would not appear to be adapted for dampening the forces experienced at the interface of the motor and carriage. Further, this reference does not provide any multiple sleeved cylinder means as the primary drive of the drill string motor along the carriage thereof.
A further earth boring apparatus which is known in the art is disclosed in U.S. Pat. No. 4,858,704. Similar to U.S. Pat. No. 4,953,638, this specification provides a drill rig moveably mounted on a track assembly. There is no discussion or contemplation of any arrangement for damping stress received at the drill motor rig from the drill string. In this reference, it would appear that the apparatus would not be well suited to actuate boring since the same does not even provide a drill string support on the drill rig carriage. Further, although the patentees have disclosed the possibility of employing fluid cylinder means as the drive source for the rig, there has been no provision for addressing the problem of cylinder sag inherent when the rig advances along the track.
A further arrangement broadly related to the subject matter of the present invention is taught in U.S. Pat. No. 5,133,418. The arrangement disclosed lacks a support for the drill string motor capable of accommodating lateral and/or elevational movement thereof. Accordingly, any stress of this variety would be, since the motor is rigidly connected to the frame, absorbed by the drill string. This may result in inaccurate boring as indicated herein previously and could also result in forces being transmitted to the connection between the drill string motor and the drive therefor. In the case where the drive may be a cylinder, this could result in cylinder damage.